For successful implantation in humans, the endometrium must be adequate prepared by steroid hormones to allow attachment of the embryo to the epithelium, passage through the epithelium, and invasion of the trophoblast into the maternal stroma. We have had a long-standing interest in the insulin-like growth factor (IGF) family and its role in the invasive phase of human implantation. IGF-II is exclusively expressed by the invading trophoblast, and it regulates restraints of invasion produced by the maternal decidua. Two inhibitors of IGF action, IGF binding protein (IGFBP)-1 and IGFBP-1, are made by the decidua. We have identified an enzyme that cleaves IGFBP-4 and decreases its affinity for IGF-II and identified it as a known protein with unknown function, pregnancy-associated plasma protein-A (PAPP-1). Its naturally occurring inhibitor is also a major product of the invading trophoblast in human pregnancy. In this grant we propose to investigate the hypothesis that IGFBP-4 proteolysis increases IGF-II bioavailability in the placental bed to enhance IGF-II action on the decidua, resulting in regulation of maternal restraints on invasion. In addition to the invasive phase, we have initiated studies relevant to paracrine dialogs between the endometrial epithelium and stroma important during the window of implantation. Our recent gene profiling of human endometrial biopsy specimens reveals marked up-regulation of IGF and wnt family mRNAs during the implantation window. Wnts are important in epithelial- mesenchymal interactions, and we have identified selective expression of wnt family members in human endometrial epithelial and stroma. IGF-II and wnt signaling may interface through a common, pathway, suggesting a role for stromal-derived. IGF-II interacting with epithelium-derived wnt on effects on the stroma during the implantation window. Herein, we propose: (1) during the invasive phase of implantation to investigate the function(s) of IGF-II, IGFBP-4, PAPP-A, and its inhibitor at the decidual: trophoblast interface; (2) during the window of implantation, to investigate the role of wnt and IGF-II signaling in epithelial-stromal communication. We work with the human model because of uniqueness of implantation in humans. These studies have relevance to infertility, ectopic pregnancy, and contraception.